Taking Down Terrorists in Court

Zainab Ahmad has prosecuted thirteen international terrorist suspects for the American government. She hasn’t lost yet.

Ahmad has probably spent more hours with Al Qaeda members and other terrorists than any other American prosecutor.

Photograph by Pari Dukovic for The New Yorker

Zainab Ahmad had a small disaster in Saudi Arabia. “I always borrowed an abaya from the legat in Riyadh,” she said. An abaya is the full-length robe that is required dress for women and girls in Saudi Arabia. “Legat” is short for the legal-attaché office, the F.B.I. presence in an American Embassy. Ahmad is an Assistant United States Attorney with the Eastern District of New York. “A button came undone during a meeting, and suddenly it was like something out of ‘Showgirls.’ ” Ahmad laughed. The Saudis were unamused. “After that, I went and bought my own abaya on Atlantic Ave.”

We were sitting in a diner on Cadman Plaza, across from the Brooklyn federal courthouse. Ahmad, who is thirty-seven, was looking litigation-ready, in a well-cut dark suit and a cream blouse. “That’s Judge Glasser,” she whispered, motioning with her eyes toward another table. “He did the Gotti trial.”

The Eastern District of New York has long been known for its work against organized crime. Since the September 11th attacks, E.D.N.Y. has also become an aggressive prosecutor of terrorism, securing more convictions than any other U.S. Attorney’s office. Ahmad’s specialty is counterterrorism, her subspecialty “extraterritorial” cases, which means that she spends a great deal of time overseas, negotiating with foreign officials, interviewing witnesses, often in prison, and combing the ground for evidence in terror-related crimes against Americans. She spends time in American prisons as well, typically with convicted jihadists. A former supervisor of Ahmad’s told me that she has probably logged more hours talking to “legitimate Al Qaeda members, hardened terrorist killers,” than any other prosecutor in America.

“They’re treasure troves of information about the networks, once they decide to coöperate,” Ahmad told me. “Some of them didn’t expect to be here, to face any consequences. Their plan was suicide. Now they’re very vulnerable. Everybody’s human. You pull the levers.” The main lever that prosecutors have with coöperators is a reduced sentence. For naïve young men, disenchanted with jihad and looking at forty years to life, that can be a powerful incentive to talk. Ahmad may ask them to testify in court. She has prosecuted thirteen people for terrorism since 2009, and has not lost a case.

That week, in the courthouse across the street, she had finished a hearing in the case of a Malian man accused of murdering an American diplomat in Niger. In December, 2000, William Bultemeier, a military attaché, was gunned down in a midnight carjacking outside a restaurant in the capital. The accused was Alhassane Ould Mohamed, also known as Cheibani, who was famed around the Sahel as a smuggler. He was arrested, and the case seemed strong. Bultemeier’s vehicle, a Toyota Land Cruiser that belonged to the Embassy, was recovered in Timbuktu, and Cheibani’s fingerprints and DNA were found inside. A security guard at an Air Afrique office testified to seeing him commit the shooting.

In 2002, though, Cheibani escaped from jail, and reportedly went to work for Al Qaeda in the Islamic Maghreb. A.Q.I.M. finances its campaigns by smuggling and by kidnapping Westerners, and Cheibani was said to have participated in the kidnapping of two Canadian diplomats in 2008. After a subsequent attack on a Saudi convoy in Niger left four dead, he was caught, tried, and sentenced to twenty years. Then he escaped again, in a mass breakout mounted by Boko Haram.

In 2012, Ahmad got the Bultemeier investigation, by then a very cold case, reassigned to E.D.N.Y. The next year, with Cheibani “in the wind,” as Ahmad put it, she obtained an indictment, and soon afterward the French Army caught him in an Al Qaeda column in northern Mali.

In Brooklyn, Cheibani’s lawyers, public federal defenders, had requested a suppression hearing, hoping to quash some of the prosecution’s evidence on constitutional grounds. Such hearings are a chance for the defense to get a preview of the government’s case. The preview that Cheibani and his lawyers got was discouraging. “They know Zainab’s reputation,” a federal prosecutor who has worked with Ahmad said. “They know their chances are not good.”

Ahmad had made numerous trips to West Africa, chasing leads, collecting evidence, interviewing potential witnesses. For the hearing, she brought in seventeen witnesses from Niger and Mali, few of whom were prepared for a New York winter. “Half of them had only sandals,” Ahmad said. “We were all frantically scraping up coats, hats, shoes. We came this close to putting a woman on the stand in a yellow hat with a pompom.” At the hearing, in the marble and mahogany grandeur of a Brooklyn federal courtroom, Cheibani was presumably astonished to see seventeen Africans ready to testify against him. On March 24, 2016, he pleaded guilty to conspiracy to commit murder, and was subsequently given a sentence of twenty-five years. “He’s not an ideological jihadist,” Ahmad said. “He’s in it for the money. But a lot of people are in it for the money, and his knowledge of the Sahel has been very valuable to A.Q.I.M.”

Knowledge is everything in counterterrorism. “Coöperators are the unsung heroes of this business,” Ahmad said. One of her former supervisors at E.D.N.Y., David Bitkower, told me, “You coöperate some kid from Minneapolis in 2009, and a couple of years later he’s going to help you prosecute an Al Shabaab commander, who is going to help you pursue defendants farther up the chain.” Ahmad considers all her time with ex-jihadists well spent. “They always know more than they think they know,” she told me. “Everything they remember helps fill in the picture.”

Trials are relatively easy, in Ahmad’s view: “There’s a neutral arbiter—a judge, a jury. You make your best argument, and they decide.” Getting an extraterritorial terrorism case charged, on the other hand, requires establishing facts to the satisfaction of an American grand jury about events that occurred, often years ago, in faraway places. For Ahmad’s cases, those places have included Afghanistan, Pakistan, Yemen, Iraq, Saudi Arabia, Tunisia, Algeria, Syria, Nigeria, Niger, Kenya, Somalia, Trinidad, Guyana, Canada, and the United Kingdom.

But the hardest part of bringing a terrorism suspect onto American soil, she says, has usually been convincing the U.S. government that it’s safe. Special approval must be obtained both from Main Justice—as government lawyers call Justice Department headquarters, in Washington, D.C.—and from the National Security Council, in the White House. The political opposition to such transfers has been entrenched for years on Capitol Hill, and has only intensified since the attempt to put Khalid Sheikh Mohammed, the alleged mastermind of the 9/11 attacks, on trial in Manhattan federal court. That effort failed, in 2010, in the face of objections from Congress and local officials.

In the Senate, the drive to oppose and defund civilian trials for accused terrorists has long been led by the Republicans Lindsey Graham of South Carolina, Chuck Grassley of Iowa, and Jeff Sessions of Alabama. “This is no way to fight a war,” the three senators and a group of their colleagues wrote, in a 2015 letter to Eric Holder, then the Attorney General. The letter referred, specifically, to several extraditions that Ahmad was involved in. The senators and their allies strongly prefer that foreign terrorists who target Americans be detained in the military prison at Guantánamo Bay and, when possible, tried by a military tribunal. In 2009, Sessions, who is now the Attorney General, added an amendment to a military spending bill titled “No Miranda Warnings for Al Qaeda Terrorists.”

Ahmad and her colleagues have been working meanwhile to develop, with considerable quiet success, a criminal-justice alternative to Guantánamo. It’s a high-wire act. The public has unique expectations of law enforcement with respect to terrorism. “When there’s a bank robbery, we try to solve the crime,” Ahmad said. “But nobody thinks our job is to stamp out bank robbery. Terrorism is different. People expect us to prevent it.” Many terror cases are difficult to make, with the strongest evidence often classified or inadmissible. “And we can’t afford to lose,” Ahmad told me. “We can’t get anything wrong. If we lost a major extraterritorial case, there might never be another chance.”

Ahmad had a multifaceted upbringing. She grew up in suburban Nassau County, Long Island, with her father and stepmother and two younger brothers, and she also lived part time with her mother, in Manhattan. Her parents had divorced, amicably, when she was an infant, and, as Zainab grew, according to her father, Naeem, “she would play Mom off against Dad, but always for one thing—to buy more books.” Her parents were part of the Pakistani diaspora, and Zainab spent summers in Pakistan and England. Visits to Pakistan were an adventure—she had dashing, rowdy cousins—but England was often a shock. “You could feel the discrimination,” she told me. “My cousins, no matter how successful or well educated, were never going to be accepted as British. People would ask me where I was from. I’d say I was American. Then they’d say, ‘Yes, but where are you really from?’ I was always so glad to get home.”

“We felt comfortable here,” Naeem told me, when I visited him and his wife, Nasrin, at their home, in East Meadow. “I felt comfortable with my neighbors, and never told my children to avoid kids because they’re Christian, Jewish—none of that.” (Most of Zainab’s friends as a child were Jewish.) Naeem, a retired engineer, is an active member of a local mosque, and has taught Sunday school since the nineteen-eighties. “I am a very religious man,” he said. “But not a religiosity man. I don’t care what other people do.”

Naeem and his first wife, Jamile, left Pakistan for Canada in the nineteen-seventies—for economic reasons, he said. But his engineering degree, from the University of Peshawar, was not recognized in Canada, so he found work investigating insurance claims. In 1977, the couple moved to New York, where Zainab was born three years later. Naeem managed a restaurant in midtown and later helped run a construction firm. His boss, who eventually became his partner, was a Hindu from India. “We’re both from the Punjab,” Naeem said. “But if there was a war between India and Pakistan we didn’t bring it home. We were the same, except he went to temple and I went to mosque.”

Zainab’s parents describe her as a cheerful, precocious child. “She never walked, she always skipped,” Jamile, who now lives in Pakistan, told me. “Her sixth-grade teacher praised her respectfulness, and that meant a lot to me. A lot. It’s difficult to raise a respectful child in the U.S.” When Zainab was eight or nine, she and Naeem read the entire Quran together, which took about a year. She didn’t understand a word, she said. Later, as an undergraduate at Cornell, majoring in health policy, she studied Arabic. “We talked every night,” Naeem said. “She would give me the gist of the Arabic. I would send her back to class with new ideas and questions.” Even as a lawyer, he said, “she sometimes uses me as a bounce-off for ideas—to see what I say.”

Naeem served lunch and tea. A few days earlier—this was last spring—there had been a Trump campaign rally in Bethpage, a couple of miles to the east. “You could hear the roaring from here,” Naeem said. “Everything but the ‘_Build the wall! _’s.” Like his daughter, Naeem has a quick tongue and a ready laugh.

Nasrin, a tall, smiling woman in her fifties, is the town clerk of Hempstead, which has a population of eight hundred thousand. She is the first elected official of South Asian extraction in New York State. While we talked, white guys in pickups parked in the driveway and came to the front door, where they conferred with Nasrin over sheaves of documents—constituent service on a rainy Saturday afternoon. The American Dream lives on Long Island.

And yet I remembered Zainab saying, “If I were fifteen now, growing up where I did—I don’t know. Everything’s changed.” She meant the level of mistrust that Muslims in America face. “When I was a kid, even though I had a funny name, and didn’t look like everyone else, it honestly took me a very long time to realize that. There was nothing that made me feel different. Substitute teachers would come, and start to take attendance, and hesitate, because my name was at the top of the class list, Ahmad. They’d say, ‘I know I’m going to pronounce this wrong.’ And the whole class would be, like, ‘Zainab. Duh.’

“Every year, in elementary school, we’d have American Heritage Day. Everybody would say where their family was from. Germany. Poland. I remember, in second grade, saying, ‘My family’s from Pakistan.’ The teacher pulled down a map, and I didn’t know where Pakistan was, even though I’d been there. I was totally embarrassed. But then I was relieved because the teacher didn’t know, either.” Ahmad laughed. “I’d kind of like to go back to a time in America when teachers didn’t know where Pakistan is.”

Jamile told me, “When Zainab was little, she wanted to be a receptionist. She loved answering the phone. Then she wanted to be a nurse. I mentioned lawyer, because my dad was a lawyer, but I wasn’t serious.” Ahmad herself is vague about how law happened. She had planned to be a hospital administrator, but things went sideways after the September 11th attacks, and she ended up at Columbia Law School, on a full scholarship. One judge she clerked for, Reena Raggi, of the Second Circuit Court of Appeals, recalls her strong academic background in finance and economics. “She excelled in a variety of areas,” Raggi told me. “Her ability to analogize. Her aptitude for solving problems. She has a deep critical mind. Zainab doesn’t come across as a hardboiled, aggressive prosecutor. She’s reserved—that’s her upbringing. She would have been successful in any field. But, I must admit, I didn’t see this coming.”

Naeem once got a call from his daughter while she was clerking for U.S. District Judge Jack B. Weinstein. It was 2006, at the end of a major Mafia trial. “Zainab was crying,” he said. “The defendant had been convicted. She said, ‘I couldn’t take it when he took off his watch and his necklace and gave them to his family.’ She had got to know these people. So I said, ‘Which side would you rather be on, the government or the defense? You’re not after the person, you’re after the truth.’ ”

When Ahmad joined the Eastern District, in 2008, she first worked on Brooklyn and Staten Island gang cases, but soon found herself drafted into a terrorism investigation that centered on a plot to blow up fuel tanks and pipelines at John F. Kennedy International Airport. The plotters, one of them a former baggage handler, were a motley quartet from Guyana and Trinidad, and the case led to both Iran and Al Qaeda. “You start following a disgruntled baggage handler, a guy who’s mouthing off in Queens,” Ahmad said. “But he has the potential to connect with serious networks—and this guy did it.” Russell Defreitas, the baggage handler, made trips to Guyana, looking to contact a senior Al Qaeda leader. When his search failed, he settled instead for Abdul Kadir, a chemical engineer and former member of Guyana’s parliament, who had transferred his allegiance to Islamist extremists in Iran. The investigators moved carefully, placing an informant with Defreitas, but not, at first, asking him to gather evidence with a tape recorder. “We weren’t sure about Guyana law, or the Guyanese, and you don’t want to blow your informant,” Ahmad said. “We’re not the intelligence community. We’re law enforcement. We have to declare we’re there. You have to figure out who you can trust. Eventually, we worked it out, and we got him recorded.”

Marshall Miller, the lead prosecutor on the case, was struck by how Ahmad took to the work. “Zainab was really good in Guyana with local law enforcement,” he told me. “She made them feel respected. Ninety per cent of prosecutors, that doesn’t come naturally to them. They want to get shit done. But the best prosecutors are born diplomats, particularly in this field. You need to be able to relate to people from all over the world.”

Miller’s team discovered links between Kadir and Mohsen Rabbani, an Iranian diplomat believed to be the mastermind of the 1994 bombing of a Jewish community center in Buenos Aires. Kadir, they determined, was planning to engage the Iranian military and special forces in his plot. When he tried to fly to Iran, they abruptly halted the investigation and had the plotters arrested. “We had to take it down,” Ahmad said. “If this were all happening in the U.S., you could afford to let it go and roll up more people. They didn’t have explosives yet. But if he goes to Iran he goes totally dark. He already had the J.F.K. plans. We couldn’t let him get away.”

At the trial of Kadir and Defreitas, in 2010, Miller assigned Ahmad to make the closing argument. She knew the case thoroughly, and had shown poise and fluency in court. In the summation, she gave a bracing description of the plotters’ intent: “Their goal was to destroy the economy of the United States. They knew that accomplishing that goal would take lives, and they didn’t care. In their view, the innocent lives lost would be mere collateral damage.”

Defreitas had testified that his tape-recorded plans to cause devastation were just empty talk. “Ladies and gentlemen, that is ridiculous,” Ahmad said. “It’s not like you find your kid brother borrowed your car and crashed it and you yell, ‘I’m going to kill you!’ Everybody realizes you are not actually going to kill your brother. You’re just blowing off steam in the heat of the moment. That is not what we’re dealing with here. . . . Russell Defreitas is doing everything he can to make his nightmare a reality.” The jury deliberated for five days. Then they convicted Defreitas and Kadir on multiple counts of conspiracy to commit acts of terrorism. Both men were sentenced to life in prison.

There are ninety-three U.S. Attorney’s offices. Of these, fewer than half a dozen are in a position to pursue extraterritorial cases. Terrorism is only one area of transnational crime, but it is easily the most high-profile. In recent years, E.D.N.Y. has in some ways overtaken its traditional rival, the Southern District, which is based in Manhattan. “Competition with S.D.N.Y. makes you kind of entrepreneurial,” Marshall Miller told me. “We’re like the scrappy little brother. Immediately after 9/11, we had, I think, zero terrorism cases. The goal was to change the program. You gotta go out there and make friends with all the agents and legats. S.D.N.Y. was haughty. They let you know they’re the best. We tried to be the guy you wanted to go out for a drink with. Friendly.” Experienced agents noted the hustle. Tara Bloesch, an F.B.I. special agent, who has completed several tours in Pakistan and is now based in Philadelphia, told me, “If there’s a way to legally establish venue, the E.D.N.Y. will do it. Maybe it’s just the airport that returning fighters land in—anything.”

When the F.B.I. has a promising investigation, it becomes like a client shopping for a lawyer. Which U.S. Attorney’s office would be most effective on this case? As Ahmad began travelling in the Middle East, Africa, and Europe, and began winning significant convictions, her stock at the F.B.I. rose. Judge Margo Brodie, of the Eastern District, who was formerly the deputy chief of the Criminal Division at E.D.N.Y., told me, “Agents were bringing their cases to the office, begging to have her take them. It never dawned on her that the reason she had so much work was that she’s so good.”

Bloesch worked closely with Ahmad on a gruelling 2015 trial, providing information about events in Pakistan. “I’ve never seen anybody work that many hours,” she said. “Everybody else kind of falls in line. We worked Saturdays, Sundays.” Celia Cohen, one of Ahmad’s co-counsels on that case, lives in New Jersey and has two young children, but she moved into Ahmad’s apartment in Manhattan for three weeks during the trial. “We hardly slept,” Cohen told me. “It was like college. We just discussed the case till we crashed and woke up with new ideas.”

Building an extraterritorial terrorism case typically requires permission from foreign governments to conduct investigations in their domains, and then assistance in apprehending suspects and transferring them to American custody. This process can involve a great many sign-offs—delicate, overlapping negotiations prone to being buffeted by political and bureaucratic winds.

When Ahmad revived the case of William Bultemeier’s murder, in West Africa, David Bitkower, her supervisor, had doubts. “That region is not a five-star destination at the best of times, and this was not the best of times,” he said. “Al Qaeda had just taken over the northern part of Mali. Zainab was bound and determined, though. It was a righteous case.” In Niger, she interviewed police officers who had dealt with Cheibani, and the owner of a garage where he had left his truck on the night of the murder. She found another eyewitness, a one-legged beggar called Toto, who was still working outside La Cloche, the restaurant where Bultemeier had eaten his last meal. The original eyewitness, the security guard, had long vanished and was presumed dead. Ahmad found him, too. “He was petrified,” she said, but ultimately agreed to testify. For that, Ahmad gave credit to her case agent, John Ross, a former New York City police officer: “Ross has incredible people skills.”

Ahmad and Ross went next to Algeria, looking for a woman who had been engaged to a Cheibani associate. Her house in Niger had been searched in the initial investigation. “Maybe we can put Cheibani in Niger,” Ahmad said. “That would be huge. Because we’ve only put him in the truck.” The woman and her daughter were a prostitute team, now living in the southern Algerian city of Adrar. “We got a lot of pushback from the Embassy on that trip,” Ahmad said. “I felt strongly that we should go, and not ask for the witnesses to come to Algiers. We’re the supplicants here.” The daughter turned out to be helpful, and Ahmad put her on the list of witnesses to be flown to Brooklyn. “But the interview process was so cumbersome there, so formal. We had to take an Algerian judge with us to her house. The defense attorneys don’t have to do that.”

But, in the view of Joshua Dratel, a New York attorney who has represented a number of high-profile terrorism defendants, it’s the government that actually enjoys an advantage in evidence-gathering. “Foreign governments won’t coöperate with us,” he said. “Foreign witnesses even won’t coöperate with us. They’re afraid that we’re really U.S. agents, or that they’ll get in trouble if they talk to us.”

Ahmad, who really is a U.S. agent, says that she also struggles to cultivate foreign witnesses. “We can’t just go knock on doors in Niger. Defense attorneys can. I need permission from the Embassy, the State Department, the Niger government. We’re a government engaged in sovereign relations with a foreign government, and in deference to them.”

Ahmad pursued the Cheibani case because, she said, it seemed both important and feasible. “It’s all triage,” she said. “It’s not like we’re going around West Africa trying to charge everybody who supports A.Q.I.M. or Boko Haram. This was the murder of an American diplomat. I remember an official in Niger saying, ‘I really hope my country will do what you’re doing if something happens to me.’ ”

Cheibani’s home town of Gao was out of reach; it lay in the part of northern Mali that was being held by Al Qaeda and its affiliates. “The A.Q.I.M. flag was flying over Gao,” Ahmad said. But the Gao policemen who had originally arrested Cheibani had fled south, and she found them outside the capital, Bamako. They told her that Cheibani had spoken freely about his crime, and that they had found parts of Bultemeier’s vehicle—a bumper, a luggage rack—in a search of his house. She felt ready to charge.

Ahmad arranged for the policemen to come to Brooklyn and appear before a federal grand jury, and in June, 2013, the jury returned a sealed indictment. A few months later, when the French Army reported capturing Cheibani, Ahmad was uncertain that it was really him. The Sahara is a big place. But, she said, “We had his biometrics, from his Bamako arrest. Turned out it was him.” The French handed Cheibani to the Malians. As Ahmad worked toward an extradition, her diplomatic skills were at full stretch. Cheibani’s criminal networks were formidable, and any of the governments involved—France, Mali, and Niger—could have halted the process at any time. Finally, she told me, the Malians said, “Yes, come and get him.” Ahmad exhaled, shaking her head. F.B.I. agents retrieved Cheibani. “They Mirandized him on the plane,” she said. “I first saw him at his arraignment. He looked much older than his photos, like he’d led a hard life. It was one of the most moving moments I’ve felt doing this work.”

I had heard from several people that Ahmad has a great rapport with juries. When I asked her about it, she seemed embarrassed. We were back at the Cadman Plaza diner—which, I’d learned, Brooklyn prosecutors call the Perp Diner. “I don’t know,” she said. “Maybe it’s because I feel comfortable with them. The mosque I went to as a kid was in Queens, and it drew people from all over Brooklyn, Long Island, the Bronx—cabdrivers, truck drivers, regular working-class people. My parents’ friends came from their mosque. When I look at these Brooklyn juries, I see the people I grew up around.”

Ahmad lives downtown, in an apartment that looks out on East Fourteenth Street. Her mother, Jamile, visits every summer. She’s an elegant woman, who had worked as a computer programmer at an insurance company in midtown for many years. She loves New York, and steps lightly through the swelter of an East Village sidewalk. “In Pakistan, we grow up street-smart,” she said. “In America, the children are so naïve. Zainab is naïve. Zainab would be shocked if I ever told a lie. ‘What?’ In Pakistan, kids would never be fazed. But I think that’s important—to irk your child. So I’m here.”

Ahmad was briefly married, to a lawyer from Jordan, but is now divorced. Though she lives alone, and travels constantly, she manages a busy, even glittering social life. “Zainab has a wider range of people she’s close to than the rest of us do,” a friend of hers, a freelance writer, told me. “She’ll throw a party at her place, and it’s cops, actors, journalists, filmmakers, doctors, businesspeople, Pakistani lawyers, academics. She doesn’t cook, but there’s always a ton of food. She’s the sort of person everybody wants to make food for. I first met her at a rooftop barbecue in the Village. It was dark, but it was like she was sunny—I can’t think of a better word for it. You see that light, and you want to get near it.”

After hours, Ahmad likes to sing karaoke at a joint on Avenue A. “She always sings lighthearted, feisty-girl songs,” her friend said. “I thought Taylor Swift was just trendy and beneath notice until I heard Zainab sing ‘Blank Space’ there with her cop friend Ed.” On cross-examination, Ahmad admitted that her signature karaoke tune is “Manic Monday,” as interpreted by the Bangles. Her youngest brother likes country music, so they belt out Luke Bryan’s “That’s My Kind of Night” on drives out to see the folks on Long Island. On road trips with her best friend from college, Shally Madan, who lives in California, Madonna, Rihanna, and the “Bend It Like Beckham” soundtrack see heavy rotation.

Ahmad seems barely to share her intensity (or much else) about her work with her nonwork friends. “She’s so offhand about it,” the freelance writer said. “She doesn’t let her work hang over her like a pall. Last year, she had just finished some very tricky case. Then we went out and sang karaoke.”

There is, of course, much about her work that Ahmad can’t discuss with anyone lacking the relevant security clearance. When I asked her, at the Perp Diner, about how an American prosecutor “coöperates” a jihadist, she drummed her fingers, shook her head, and finally came up empty. “Everybody I’ve flipped is still under seal.”

On certain mornings, when she’s in town, her workday starts with a walk across town to Chelsea, where the New York Joint Terrorism Task Force has its headquarters. One floor of the building is a Sensitive Compartmented Information Facility, a secure area that blocks surveillance. Ahmad leaves her phone outside. Inside, she can speak freely about cases by teleconference with intelligence operatives, diplomats, and military officers with top-secret clearance all over the world.

In combatting terrorism, Ahmad says, there is no conflict between the military and the civilian criminal-justice system. She works closely with the Pentagon, and defers to the military where it has jurisdiction. In one case, she was pursuing an Iraqi-Canadian charged in the murder of five American soldiers, killed by suicide bombers whom he had helped travel from Tunisia to join Al Qaeda in Iraq. The man was living in Edmonton, and Canada, like most countries, will not consider an extradition request from the U.S. military as long as Guantánamo remains open. To persuade the Canadians, she had to gather evidence in Iraq, which was then unstable enough that Ahmad and an F.B.I. colleague had to take cover from daily rocket attacks. As Ahmad investigated, she was transported in military helicopters. In Mosul, she stayed on a U.S. military base, and soldiers brought witnesses to the perimeter for interviews. “I think military investigators often see us as finishers,” she told me. “They may have a lot of evidence on somebody. We’ve got the machinery, and the credibility, to charge and try that person.” After four years, she persuaded Canada to extradite the man.

Some of the indictments that Ahmad has obtained remain sealed, usually because the suspect is still at large, and I suspect—Ahmad says she disagrees—that this can produce conflicts of interest, if, say, the Pentagon and the C.I.A. are trying to kill the same individuals she is trying to haul into court. This seems to have been the case with Mohanad Mahmoud al-Farekh, a Texan who became a high-ranking Al Qaeda leader. The Justice Department wanted to prosecute him, but the Pentagon and the C.I.A. reportedly wanted to put him on a kill list, arguing that he could not be captured. As it turned out, Farekh was captured by Pakistani forces in 2014 and handed over to the U.S., where Ahmad charged him, under seal, the following year. He now awaits trial in Brooklyn.

For Ahmad, the more complex collaboration is with U.S. intelligence agencies. Spies and prosecutors investigating terrorists are often after the same information, but spooks cannot, for obvious reasons, be called as witnesses. “We discovered, as terrorism cases ramped up, that we needed to put in a second informant,” Marshall Miller told me. “We had to have one who could testify in court.” If Ahmad uses evidence gathered by intelligence agencies in a public trial, she risks revealing sources and classified data. Prosecutors are obliged to ask permission to use this evidence, and, as with extraditions, these are not negotiations that can be conducted by e-mail. “You have to go there, whether it’s to Langley or Nigeria, and meet with people, explain what you want, gain their trust,” she said.

Any exculpatory evidence must be disclosed to the defense, though attorneys need security clearances to see classified information. “They’re usually disappointed,” Ahmad said. “They want to know where the real Super Secret Squirrel stuff is. But there is no real Super Secret Squirrel stuff. We wish.”

Joshua Dratel, the New York attorney, says that, in counterterrorism cases, the government’s control of information gives it another advantage. “By making juries anonymous, we’re telling jurors that the defendant is really dangerous,” he said. “I’ve had the government put an anonymousexpert on the stand. The standard of probable cause for surveillance is diluted in national-security cases. They don’t even need a warrant for overseas wiretaps. In the past decade, we see much less classified information, and we have to get a lot of it through the judge, who knows nothing about the case.”

“We were a bit desperate before Zainab showed up here,” Mark Smith, the head of covert policing for the Greater Manchester Police, said. British intelligence had caught wind of an Al Qaeda operation in 2008. About a dozen men from Pakistan had entered the country on student visas, registered for classes, and immediately quit school. Surveillance showed them to be scouting a range of public venues, eventually concentrating on the Arndale Centre, a large shopping mall in Manchester that, in 1996, was the target of an I.R.A. truck bomb that devastated much of the city’s retail district. Abid Naseer, a graduate student from Peshawar, with a B.A. in English literature, began to regularly e-mail an Al Qaeda handler in Pakistan. He wrote that he was planning to get married soon, but in his daily rounds there was no sign of a fiancée, or of marriage preparations. This was a code that the Brits had seen before. The wedding day would be the attack day.

“We devoted all of our counterterrorism resources to this surveillance,” Smith, who was then leading the region’s terror-investigation force, told me. “We had twenty-five, twenty-six teams trying to watch nine guys. What if one of these guys goes off the radar? The risk was high. When we saw the attack-dates e-mail, we had to strike.”

Law enforcement pounced too soon, though. From the intercepted e-mails, and from quantities of flour and oil found in Naseer’s flat—Al Qaeda teaches operatives how to build bombs starting with flour and oil—the authorities inferred that the group had planned to make bombs with chemical detonators and an organic charge, similar to those used by the bombers who struck three Tube trains and a London bus in 2005, killing fifty-two. But no bomb-making chemicals were found, and the British press grew increasingly dubious. The government, hoping to make the whole thing go away (the exchange-student business in Britain is large and lucrative, Smith pointed out), decided to deport the suspects rather than prosecute. The detectives on the case were horrified when they heard the news, at the prosecutor’s office. “I couldn’t accept it,” Smith told me. “They nearly called security to remove us.”

Naseer fought his deportation, arguing that a return to Pakistan would be unacceptably dangerous, and he won the right to stay. But by then the Americans had become interested in his case, particularly after British intelligence alerted the F.B.I. that the e-mail account that Naseer had been reporting to—the Al Qaeda handler in Pakistan, e-mailing as sana_pakhtana@yahoo.com—had started receiving e-mails again, this time from a jihadist in the United States who was asking for bomb-making instructions. “I nearly crashed the car when I heard that,” Smith told me. Ahmad said, “It was really bad op sec”—operational security—“on Al Qaeda’s part, to use the same Yahoo address. I mean, come on.” The U.S. plotters were arrested. Ahmad headed to Manchester.

“When Zainab walked in the room, we said, ‘Crikey, she looks awfully young. Is this a junior sent here to fact-find?’ ” Smith said. “Within a few minutes, though, it was, like, ‘Whoa, she knows what she’s doing.’ There was no comparison with U.K. prosecutors. Zainab stayed four days with us on that first visit, and left us a big list of evidence she wanted, and exactly how she wanted it packaged up.”

Ahmad’s goal was to demonstrate that Naseer’s plot was part of an international conspiracy, allegedly organized by Al Qaeda in Pakistan, to bomb targets in the United Kingdom, Denmark, and the United States. The would-be U.S. bombers were three young men who had been classmates at Flushing High School, in Queens, and then, in 2008, travelled together to Pakistan to join the Taliban. They ended up instead with Al Qaeda, from whom they received military training and, ultimately, orders to return home and carry out suicide bombings. They were of more use to the cause, they were told, using their local knowledge to attack New York City than they were in Muslim lands. After considering Grand Central Terminal, Times Square, and other landmarks, they settled on bombing subway trains at rush hour. By now, the authorities were monitoring their phones, however, and reading their e-mails to Al Qaeda, which used much of the same code that Naseer had used, including an upcoming “wedding.”

One of the U.S. plotters, Najibullah Zazi, an Afghan-American, was working as an airport-shuttle driver in Denver. Following instructions that he had e-mailed to himself from Pakistan, he bought hydrogen peroxide and acetone from local beauty-supply outlets, rented a hotel suite in nearby Aurora, and used the kitchen to cook up triacetone triperoxide, a detonator explosive similar to that used in the London attacks. He tested the mixture in the hotel parking lot. It exploded, as he had hoped. Zazi packed the detonator explosives in a rental car and drove to New York.

As he crossed the George Washington Bridge, police stopped him, at the request of the F.B.I., but they failed to find the jar of explosives in the car. Zazi was spooked. Then his rental car got towed in Queens, with his computer, containing all the bomb-making instructions and incriminating e-mails, inside. Zazi flushed the explosives down a toilet and flew back to Colorado, where he was arrested almost immediately. His accomplices were detained a few months later, and, in 2010, Zazi pleaded guilty to multiple terrorism violations; one accomplice, Zarein Ahmedzay, also pleaded guilty. Zazi and Ahmedzay are still awaiting sentencing, as their coöperation with law enforcement continues to be useful. (The third member of their plot, Adis Medunjanin, a Bosnian-American, pleaded not guilty. He was convicted, in 2012, in Brooklyn federal court, and sentenced to life in prison.)

Abid Naseer fought extradition from the U.K. but lost, arriving in Brooklyn in early 2013. Ahmad, preparing to try him, debriefed Zazi and Ahmedzay at length. They had been in Peshawar in November, 2008, when Naseer was also there. The same Al Qaeda “external-operations” team that tasked Zazi and his friends with a martyrdom operation had commanded Naseer. Ahmad planned to call Zazi and Ahmedzay as witnesses. They could fill in the picture of Al Qaeda’s training operation in Pakistan from the inside.

The Naseer trial started in February, 2015. David Bitkower, who was Ahmad’s supervisor during the first phase, told me that it was a tough case. “It was largely circumstantial,” he said. “There was no smoking gun. It was all in the argument. You can easily lose.” But Ahmad had gathered significant new evidence. Computer forensics had deepened the analysis of Internet and phone records. Ahmad tied the plots, furthermore, to Al Qaeda’s top leadership, through documents seized in Osama bin Laden’s hideout in Abbottabad, Pakistan, which had not been seen publicly before. In a letter to bin Laden, written in early 2009, Saleh al-Somali, Al Qaeda’s external-operations chief, reported, “We had sent a number of brothers to Britain, Russia, and Europe on condition that their work will be completed and ready before the end of the year.” When Mark Smith, the Manchester detective, heard those words, he said, “We knew immediately they were talking about our guys.”

Naseer represented himself, and did a credible job, though Judge Raymond J. Dearie warned him not to waste time arguing to the jury that the United States lacked jurisdiction in his case. By Act of Congress, the U.S. has broad jurisdiction to investigate and prosecute terrorism offenses anywhere in the world. Foreign investigations require the permission of the national authorities, of course, but in this case Ahmad and her team had received extensive support from the British. She called Manchester police officers and MI5 agents as witnesses, and they gladly appeared, wearing “light disguise”—wigs, fake beards, makeup—because they were still working undercover. Security for the trial was heavy. Naseer was not allowed to rise from the defense table except when summoned by the Judge; Ahmad and her colleagues were bound by the same rule, lest the jury infer that the defendant was considered unusually dangerous by the court.

“He was a soldier,” Ahmad said later, of Naseer. “Totally controlled, ice-cold, well trained. He tried to be charming to witnesses, even smiled at the jury.”

Naseer, who is powerfully built, had a bushy beard, and eyes that, at least in photographs, did not look capable of effectively supporting a smile. While acting as his own advocate, he spoke about himself in the third person. There was no “I,” only “Naseer.”

It was a bizarre case, turning largely on the meaning of a handful of e-mails between Naseer and the handler, who was code-named Sohaib. Naseer contended that the e-mails were innocent banter with a stranger whom he had met in an Internet chat room. He was looking for a wife, discussing his prospects. The prosecution contended that the e-mails were in code, and Ahmad subjected them to a probing read. In e-mails, Naseer and Sohaib agreed that a car would be useful for married life; that meant the plan called for a car bomb, Ahmad said. Sixty-one photographs of a chain store called Next and its surroundings had been saved to a draft e-mail file, which was available to his co-conspirators. This, she said, was where the bomb would be detonated. The photos suggested a second strike: panicked shoppers would stampede into the blast paths of backpack bombs set deeper in the Arndale Centre, which sees seventy thousand people on a busy day.

Naseer’s e-mails to Sohaib described a meandering courtship. He wrote that he met Huma, the first object of his affections, at a bus stop, and that he found her “very weak and difficult to convince.” She worked in a cosmetics shop. According to Ahmad, “Huma” stood for hydrogen peroxide, a bomb ingredient found in beauty products (the cosmetics shop) in a diluted, or weak, form. Extracting it in sufficiently concentrated form is a challenge—it’s “difficult to convince.” Nadia, another woman of interest, was more like it. “Nadia is crystal clear girl, and it won’t take long to relate with her,” Naseer wrote to Sohaib. “Nadia” was nitrate, Ahmad explained. Ammonium nitrate, a high-order explosive found in some artificial fertilizers, is a white crystal solid in its pure form. (Timothy McVeigh used a fertilizer bomb to kill a hundred and sixty-eight people and injure more than five hundred in Oklahoma City, in 1995.) The ammonium-nitrate detonator that Naseer settled on could be quickly assembled. “These are stilted descriptions of women, but they’re pretty good descriptions of bombs,” Ahmad told the jury.

Ahmad teased out the absurdity of Naseer’s romances. Huma, he wrote, seemed unwell. She had lost weight. This was two days after she first gave him the cold shoulder at the bus stop. “How much weight can somebody possibly lose in two days?” Ahmad asked. “On top of that, it’s December in northern England. Huma is not going to be standing at a bus stop in a bikini where you can count her ribs.”

Using a precise breakdown of Naseer’s browsing history and phone records, Ahmad showed that, on a trip to Pakistan, ostensibly to visit his sick mother, he contacted two of his co-conspirators in Britain, men whom he claimed he barely knew. He then “went dark” for two weeks, during which, Ahmad suggested, he visited the Federally Administered Tribal Areas, the rugged hinterlands along the Afghanistan border where Al Qaeda has its training camps. Ahmad brought Najibullah Zazi to the witness stand to describe for the jury his own training in the camps, where he learned how to handle an AK-47 and how to build bombs. One design—the kind “the guys in London used” in 2005—was wired through the pockets of a specially made shirt. Another, which he preferred, was to be carried in a backpack and wrapped in ball bearings for, as he put it, “the casualty purpose.”

Ahmad never mentioned her own familiarity with Pakistan—that her father had gone to university, for instance, in Naseer’s home town, Peshawar. But she spoke with authority about how Peshawar had been changed by the American invasion of Afghanistan, and of how many Pashtuns—the region’s dominant ethnic group, to which Naseer belongs—had felt humiliated by the occupation, inspiring some young men to join Al Qaeda to seek revenge. Mark Smith, the Manchester detective, who watched the trial, said, “Just the way she pronounced the names of the towns in Pakistan, you knew she wasn’t guessing.”

Naseer returned to England, still on a student visa. He never went to school. Instead, he spent much of his time online, Instant Messaging and visiting Muslim dating sites. But he never e-mailed his Al Qaeda handler from his personal e-mail address, or even from his own computer. For that, he went to an Internet café, where he habitually used the same public computer, and took care to use his operational accounts only to e-mail his handler. “This is Al Qaeda tradecraft,” Ahmad said.

Naseer’s last e-mail to Sohaib, sent on April 3, 2009, announced that he would soon be married. “I met with Nadia family and we both parties have agreed to conduct the Nikkah after the 15th and before the 20th of this month . . . you should be ready between those dates.” A nikkah is a wedding ceremony. According to Ahmad’s minute-by-minute reconstruction of the day, this e-mail was drafted, loaded on a thumb drive, and carried to the Internet café. At his usual terminal, Naseer began listening, on his phone, to a nasheed—a religious or spiritual chant. Ahmad played the nasheed for the jury, and then read a translation from the Arabic: “We are marching towards them. With turbans that will become their burial garments. They spilled their blood generously and with love. Looking forward to death in large numbers.” Naseer copied the document from the thumb drive into an e-mail and pressed Send. The attack was on, and Al Qaeda knew enough about its timing and location to prepare to take credit.

Naseer claimed that he didn’t realize Sohaib was a terrorist. But, while Zazi was on the stand, Ahmad used his testimony to establish that Naseer’s pen pal was the same handler, with the same Yahoo address, who had directed the Zazi team’s efforts to bomb New York subway trains.

In her closing remarks, Ahmad told the jury that Naseer’s demeanor alone during his testimony showed that he knew Sohaib and also knew that Sohaib was Al Qaeda: “Ask yourself, did anything he said or did, did any look that glanced over his face, suggest any shock or horror or surprise at the fact that his random Internet buddy Sohaib, who he thought was just a fun guy to exaggerate his love life to, was actually a member of Al Qaeda? Did anything he said or did suggest that he hadn’t known that all along? No, I suggest to you that it did not. He didn’t express any shock, any regret, any upsetness, any holy-crapness at the fact that he had just found out in this courtroom that he had been e-mailing Al Qaeda.”

Ahmad’s summation was three and a half hours long. She remembers looking at her notes only once. James McGovern, who was the chief of the Eastern District’s Criminal Division until last year, told me, “It was the summation of a lifetime.” Ahmad had called former Al Qaeda operatives; British secret agents; experts in explosives, computer forensics, Arabic, Pashto, and Al Qaeda’s structure; the F.B.I. agent who secured the bin Laden documents; even a Norwegian detective who could link, through shared e-mail accounts, the Manchester plot with a plot to bomb a Copenhagen newspaper office. Ahmad’s ability to connect with the jury was critical. “You want to project: I am the most reasonable person in the room,” McGovern said. “Zainab excels at that. Jurors believe that they would see eye to eye with her about things. People want to say, ‘That really impressive person, I want to be in agreement with that person.’ ” Ahmad’s proposition about Naseer was simple, in the end: “This man wanted to drive a car bomb into a crowded shopping center and watch people die.” After one day of deliberation, the jury agreed. Naseer was convicted on all counts and, in November, 2015, he was sentenced to forty years.

Last spring, Loretta Lynch, as Attorney General, asked Ahmad to come work at Main Justice. Ahmad took a leave from E.D.N.Y. and moved to Washington, where her brief included transnational organized crime and international affairs. She travelled frequently—not to dusty towns in the Sahara or prisons in Saudi Arabia but to foreign capitals. She briefed senators, represented the Justice Department at the White House, and led a delegation to Trinidad to address the outsized flow of fighters joining ISIS from there. Supervising about seventy prosecutors, she oversaw critical investigative, charging, and litigation decisions.

Soon after Sessions replaced Lynch, he demanded the immediate resignations of all U.S. Attorneys who remained from the Obama years. Since U.S. Attorneys are the only political appointees in their offices, the work of most career prosecutors went on. But Ahmad, watching the transition from up close, saw a wholesale reorientation of Justice Department priorities. Under Sessions, the themes would be immigration enforcement, a revived federal war on drugs, and the abandonment of initiatives to reduce civil-rights abuses in American police departments. Certainly, extraterritorial terrorism prosecutions would be a nonstarter.

Sessions has repeatedly expressed his desire to see accused terrorists dealt with by military commissions rather than “try them in a normal criminal court.” President Trump has repeatedly declared his enthusiasm for expanding the military prison at Guantánamo, which has not received a new inmate in nine years and presently holds only forty-one prisoners. “We’re gonna load it up with some bad dudes, believe me,” Trump told a campaign rally last year. In February, a draft executive order directing the Pentagon to send captured isis fighters to Guantánamo was leaked to the Times.

It is not yet clear how all these new inmates will be captured. But it is clear that the military commissions at Guantánamo have failed miserably. Since the September 11th attacks, federal criminal courts have convicted more than six hundred people on charges related to international terrorism. The Guantánamo commissions have convicted eight, with three of those convictions vacated or overturned on appeal, and one partially overturned. More prisoners have died in the camp than have been convicted there.

Many successful terrorism prosecutions in recent years, moreover, have followed extraditions that would not have occurred if Guantánamo and its military commissions had remained an option. Abid Naseer and dozens of other convicted terrorists now serving U.S. prison sentences would instead be free—still on the battlefield, as it is said—because our main counterterrorism partners, including the United Kingdom, Canada, Germany, and the Netherlands, refuse to provide evidence or to coöperate with extradition requests unless a suspect is to be tried in a criminal court.

But the Trump Administration seems less interested, so far, in parrying threats than in demonizing Muslims, particularly immigrants and refugees. Besides everything else, this is a strategic mistake. As Ahmad says, “America is the most successful country in the world at integrating immigrants, and that helps keep us safe. Immigrant communities in Europe are much more ghettoized, much less warmly accepted. We do have a problem with people trying to join ISIS, but the number of people going from Belgium dwarfs the number going from here, even in absolute terms, let alone relative to our populations.”

The “threat stream” emanating from Islamist extremism has not abated. Al Qaeda branches continue to wreak havoc in the Arabian Peninsula, North Africa, West Africa, and Syria. Boko Haram’s depredations ravage much of West Africa, Al Shabaab thrives in the Horn of Africa, and the Taliban is steadily regaining ground in Afghanistan. But, at the moment, none of these movements expend much energy on staging attacks in the West. The Islamic State is another story. Its online appeals to sympathizers in the Dar Al-Kufr—the territory of disbelief—continue to find vulnerable, disturbed individuals prepared to act. “It’s so hard to combat, especially with the rise of encrypted communications,” Ahmad said. “We can take down networks, but only if there are networks.”

Ahmad returned to E.D.N.Y. in April. She and her colleagues remain deep in debate over what to do with jihadists returning from the battlefields of Syria and Iraq. “When should we prosecute? Material support for ISIS is a crime, but can we make good cases? Can these guys be rehabilitated? How useful is their intel? If they’re not in custody, what level of surveillance?”

The success of U.S. federal prosecutors in rolling up terrorist networks is not widely appreciated. The leadership of core Al Qaeda has, by all accounts, been decimated. Drone strikes have been important to that progress, but their success, and the fact that civilian casualties have not been even more extensive, is entirely due to good intelligence, most of it provided by informants. Ahmad thinks that popular culture tends to misunderstand the process, and the limited utility of drone strikes. “ ‘Zero Dark Thirty’ got a crucial point wrong,” she told me. “It wasn’t stopping torture that stopped intel. It was stopping interrogation. It was going to droning, to killing. You get no intel from corpses.”

Currently, Ahmad has two terrorism defendants in custody awaiting trial. One is the Iraqi-Canadian whom the Canadians took four years to transfer to the U.S. The other is Mohanad Mahmoud al-Farekh, the Texan who was captured in Pakistan while a debate raged in Washington over targeting him with a drone strike. (This list does not include, of course, suspects whose indictments are under seal, some of whom may already be in custody and coöperating.) Ahmad told me that she may hand over these two defendants to another prosecutor. She wouldn’t do so if they were difficult cases to make—that would be bad form—but the evidence in both is very strong.

A federal prosecutor who has worked with Ahmad, and who declined to be named, acknowledged the risk of extending the protections of the U.S. legal system to accused jihadists. “If you bring a member of Al Qaeda here from Mali or Nigeria and that person is acquitted, they’ll probably file an asylum claim or a Convention Against Torture claim, saying Al Qaeda or the government back home is going to hurt them. And, the next thing you know, you’re standing next to that person in Starbucks.”

Ahmad pondered that image for a long minute. Finally, she said, “I think we’re safer even if the guy ends up next to you at Starbucks. I’ll take that as a cost of doing business when we’re putting incredibly dangerous people in jail from more successful cases. Also, if he’s done time here and then is released and stays, he’ll be under surveillance. But that has not happened. Not once.” ♦

A previous version of this article misspelled the name of Cheibani’s home town.

This article appears in the print edition of the May 15, 2017, issue, with the headline “A Righteous Case.”

William Finnegan has been a contributor to The New Yorker since 1984 and a staff writer since 1987. He is the author of “Barbarian Days.”